Roller milling tool units as described above are commonly known and reliably in use. They are widely used on center lathes for the smoothing of lathe produced work pieces. When needed, the lathe operator manually clamps such a unit onto the lathe support and removes it again after the work is done. In addition to the rolling tool such known units comprise a hydraulic device connected to the tool by pipes or hoses. Such units further comprise their own pump-motor components for producing the necessary pressure. In this way, the known roller milling tool unit consists of a rolling tool, an apparatus for the generation of the necessary hydraulic pressure, and the means for connecting these elements to the tool. Such hydraulically operated rolling units therefore are not suitable for use on machines with an automatically or manually controlled tool change during the performance of a machining operation.